diff --git a/tdd_for_embedded_c/chapter04/Makefile b/tdd_for_embedded_c/chapter04/Makefile
new file mode 100644
index 0000000..62e823d
--- /dev/null
+++ b/tdd_for_embedded_c/chapter04/Makefile
@@ -0,0 +1,74 @@
+# ==========================================
+#   Unity Project - A Test Framework for C
+#   Copyright (c) 2007 Mike Karlesky, Mark VanderVoord, Greg Williams
+#   [Released under MIT License. Please refer to license.txt for details]
+# ==========================================
+
+#We try to detect the OS we are running on, and adjust commands as needed
+ifeq ($(OS),Windows_NT)
+	CLEANUP = del /F /Q
+	MKDIR = mkdir
+	TARGET_EXTENSION=.exe
+else
+	CLEANUP = rm -rf
+	MKDIR = mkdir -p
+	TARGET_EXTENSION=
+endif
+
+
+UNITY_ROOT=../../../../Unity
+C_COMPILER=gcc
+
+CFLAGS = -std=c11
+CFLAGS += -Wall
+#CFLAGS += -Wextra
+CFLAGS += -Werror
+CFLAGS += -Wpointer-arith
+CFLAGS += -Wcast-align
+CFLAGS += -Wwrite-strings
+CFLAGS += -Wswitch-default
+CFLAGS += -Wunreachable-code
+CFLAGS += -Winit-self
+CFLAGS += -Wmissing-field-initializers
+CFLAGS += -Wno-unknown-pragmas
+CFLAGS += -Wstrict-prototypes
+CFLAGS += -Wundef
+CFLAGS += -Wold-style-definition
+CFLAGS += -Wmissing-prototypes
+CFLAGS += -Wmissing-declarations
+CFLAGS += -g
+CFLAGS += -ftest-coverage
+CFLAGS += -fprofile-arcs
+
+TARGET_BASE=test_leddriver
+TARGET = $(TARGET_BASE)$(TARGET_EXTENSION)
+SRC_FILES=\
+	$(UNITY_ROOT)/extras/fixture/src/unity_fixture.c \
+	$(UNITY_ROOT)/src/unity.c \
+	../test/LedDriverTest.c \
+	../test/LedDriverTestRunner.c \
+	../test/AllTests.c \
+	../src/LedDriver.c
+
+INC_DIRS=-I$(UNITY_ROOT)/src -I$(UNITY_ROOT)/extras/fixture/src
+SYMBOLS=
+
+
+all: clean tests
+
+
+.PHONY: tests
+tests: build/$(TARGET)
+
+build/$(TARGET):	test/*.c src/*.h src/*.c
+	@echo "Compiling"; cd build; $(C_COMPILER) $(CFLAGS) $(INC_DIRS) $(SYMBOLS) $(SRC_FILES) -o $(TARGET)
+	@echo "Running tests"; ./build/$(TARGET)
+	@echo "Preparing coverage"; cp build/LedDriver.gc* src/
+	@echo "Running coverage"; cd src; gcovr -r . -b -p --html --html-details -o ../build/cover/test.html
+	@echo "Clearing intermediate files"; rm src/*.gc* build/*.gc*
+
+
+.PHONY: clean
+clean:
+	@echo "Cleaning $<"; $(CLEANUP) build/$(TARGET) build/*.* build/cover/*
+
diff --git a/tdd_for_embedded_c/chapter04/src/LedDriver.c b/tdd_for_embedded_c/chapter04/src/LedDriver.c
new file mode 100644
index 0000000..f3436b9
--- /dev/null
+++ b/tdd_for_embedded_c/chapter04/src/LedDriver.c
@@ -0,0 +1,30 @@
+#include "LedDriver.h"
+
+
+
+static uint16_t *ledsAddress;
+
+
+static uint16_t convertLedNumberToBit(int ledNumber) {
+  return 1 << (ledNumber - 1);
+}
+
+
+void LedDriver_Create(uint16_t *address) {
+  ledsAddress = address;
+  *ledsAddress = 0x0000;
+}
+
+
+void LedDriver_Destroy(uint16_t *address) {
+}
+
+
+void LedDriver_TurnOn(int ledNumber) {
+  *ledsAddress |= convertLedNumberToBit(ledNumber);
+}
+
+
+void LedDriver_TurnOff(int ledNumber) {
+  *ledsAddress = 0x0000;
+}
diff --git a/tdd_for_embedded_c/chapter04/src/LedDriver.h b/tdd_for_embedded_c/chapter04/src/LedDriver.h
new file mode 100644
index 0000000..662d639
--- /dev/null
+++ b/tdd_for_embedded_c/chapter04/src/LedDriver.h
@@ -0,0 +1,8 @@
+#include <stdint.h>
+
+
+
+void LedDriver_Create(uint16_t *address);
+void LedDriver_Destroy(uint16_t *address);
+void LedDriver_TurnOn(int ledNumber);
+void LedDriver_TurnOff(int ledNumber);
\ No newline at end of file
diff --git a/tdd_for_embedded_c/chapter04/test/AllTests.c b/tdd_for_embedded_c/chapter04/test/AllTests.c
new file mode 100644
index 0000000..c138024
--- /dev/null
+++ b/tdd_for_embedded_c/chapter04/test/AllTests.c
@@ -0,0 +1,15 @@
+#include "unity_fixture.h"
+
+
+static void RunAllTests(void)
+{
+
+  RUN_TEST_GROUP(LedDriver);
+
+}
+
+
+int main(int argc, const char * argv[])
+{
+  return UnityMain(argc, argv, RunAllTests);
+}
diff --git a/tdd_for_embedded_c/chapter04/test/LedDriverTest.c b/tdd_for_embedded_c/chapter04/test/LedDriverTest.c
new file mode 100644
index 0000000..987d67e
--- /dev/null
+++ b/tdd_for_embedded_c/chapter04/test/LedDriverTest.c
@@ -0,0 +1,56 @@
+#include "unity_fixture.h"
+#include "../src/LedDriver.h"
+
+
+TEST_GROUP(LedDriver);
+
+
+static uint16_t virtualLeds;
+
+
+TEST_SETUP(LedDriver) {
+  LedDriver_Create(&virtualLeds);
+}
+
+
+TEST_TEAR_DOWN(LedDriver) {
+}
+
+
+TEST(LedDriver, LedsOffAfterCreate) {
+
+  uint16_t virtualLeds = 0xFFFF;
+  LedDriver_Create(&virtualLeds);
+
+  TEST_ASSERT_EQUAL_HEX16(0x0000, virtualLeds);
+
+}
+
+
+TEST(LedDriver, TurnOnLedOne) {
+
+  LedDriver_TurnOn(1);
+
+  TEST_ASSERT_EQUAL_HEX16(0x0001, virtualLeds);
+
+}
+
+
+TEST(LedDriver, TurnOffLedOne) {
+
+  LedDriver_TurnOn(1);
+  LedDriver_TurnOff(1);
+
+  TEST_ASSERT_EQUAL_HEX16(0x0000, virtualLeds);
+
+}
+
+
+TEST(LedDriver, TurnOnMultipleLeds) {
+
+  LedDriver_TurnOn(8);
+  LedDriver_TurnOn(9);
+
+  TEST_ASSERT_EQUAL_HEX16(0x0180, virtualLeds);
+
+}
diff --git a/tdd_for_embedded_c/chapter04/test/LedDriverTestRunner.c b/tdd_for_embedded_c/chapter04/test/LedDriverTestRunner.c
new file mode 100644
index 0000000..89c9674
--- /dev/null
+++ b/tdd_for_embedded_c/chapter04/test/LedDriverTestRunner.c
@@ -0,0 +1,11 @@
+#include "unity_fixture.h"
+
+
+TEST_GROUP_RUNNER(LedDriver) {
+
+  RUN_TEST_CASE(LedDriver, LedsOffAfterCreate);
+  RUN_TEST_CASE(LedDriver, TurnOnLedOne);
+  RUN_TEST_CASE(LedDriver, TurnOffLedOne);
+  RUN_TEST_CASE(LedDriver, TurnOnMultipleLeds);
+
+}